Hydrocarbon polymers, particularly ethylene-alpha olefin copolymers, are in widespread use as viscosity index (VI) improving additives for oil compositions, particularly lubricating oil compositions. A substantial body of prior art exists directed towards further reacting these ethylene-alpha olefin copolymer VI improvers to form a multi-functional VI improver.
This multi-functional VI Improver additive is used to improve not only the VI properties of the oil but often to also impart dispersancy so as to suspend soot or sludge that may form during the operation or use of the lubricant in engines. Other multi-functional VI improvers have also been reported to impart antiwear and antioxidant properties, both of which are very useful for sustained engine operation.
OEMs often set various limits for maximum sulfur, phosphorus, and/or sulfated ash levels for “new service fill” and “first fill” lubricants. For example, in some countries, when used in light-duty passenger-car internal combustion engines, the sulfur levels are typically required to be at or below 0.30 wt. %, the phosphorus levels at or below 0.08 wt. %, and the sulfated ash content at or below 0.8 wt. %. The maximum sulfur, phosphorus and/or sulfated ash levels may differ, however, when the lubricating compositions are used in heavy-duty internal combustion engines. For example, the maximum sulfated ash level may be as high as 1.6 wt. % in heavy-duty internal combustion engines. Such lubricating oil compositions are also referred to as “medium SAPS” (i.e., medium sulfated ash, phosphorus, and sulfur). When the maximum sulfated ash level is as high as 1.0 wt. %, the lubricating oil compositions are referred to as “low SAPS” lubricating oil compositions, e.g., for gasoline engines, and “LEDL” (i.e., low emission diesel lubricant) oil compositions for diesel engines. The lubricating oil composition must continue to provide the high levels of lubricant performance, including adequate detergency.
Historically, TBN has been provided by overbased detergents that introduce sulfated ash into the composition. It would be advantageous to provide a lubricating oil composition with a high level of TBN using a TBN boosting component that does not contribute sulfated ash. As highly basic components are known to induce corrosion and, in some cases reduce the compatibility between lubricating oil compositions and the fluoroelastomeric seal materials used in engines, it would be preferable to provide such a component that does not induce corrosion and, preferably, does not adversely affect seals compatibility. Tertiary amine compounds as well as hindered secondary amine compounds offer such a solution while at the same time increasing the TBN of lubricating oil compositions without introducing sulfated ash.
Thus, herein we report the synergistic combination of a dispersant-type viscosity improver and a tertiary amine compound for improving wear in an internal combustion engine.
This combination surprisingly showed improved cam wear characteristics compared to formulations without a tertiary amine compound.